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On Sat, Oct 19, 2013 at 8:25 PM, Mark Knecht <markknecht@×××××.com> wrote: |
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> OK, it's a good idea just to have a Konsole terminal open. That might |
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> catch something. |
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I'm not sure if panics show up in konsole. With a virtual console the |
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kernel actually outputs the message. Konsole under X11 is entirely |
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user-mode and I'm not sure that ANY user-mode code can ever run after |
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a panic. |
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I think a virtual console is a better bet. |
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> OK, so I remember years ago debugging something for Ingo Molnar using |
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> the serial console, but in those days it was a real serial console on |
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> a real serial port. None of my machine have those ports anymore. There |
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> must be a more modern version of doing that. I'll go look for info. |
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> Ethernet? USB? We've recently moved and the only other machine I've |
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> got here at the apartment is a Gentoo laptop. |
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That you'd have to look into. I'm not sure if the kernel can handle a |
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serial console on a PL2302/etc. It might - it is all kernel-mode I |
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think. You'd have to attach it to another device running a terminal |
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emulator, assuming you don't have a vt100/etc lying around. |
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> There's a gentoo.wiki.org page here: |
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> |
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> http://wiki.gentoo.org/wiki/Kernel_Crash_Dumps |
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> |
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> The setup looks reasonably straight forward so I've reconfigured |
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> 3.10.17 following those instructions. |
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Yeah, I forgot - that was actually started based on my blog entry, |
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actually. It may very well have been improved on since. |
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> |
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> One question for now. In the Kernel Hacking section there's an option |
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> for "Detect Hard and Soft Lockups" which on the surface looks like a |
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> good thing to turn on but it's not mentioned in these instructions. |
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Probably not a bad idea. |
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> When turned on it has options for Panic (Reboot) for both types. Seems |
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> like I probably want that all turned on? |
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You could try setting it to no and see if you actually can capture any |
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meaningful logs that way - there is a chance you could recover your |
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system without rebooting. However, a panic would be the only real |
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sure way to ensure a dump. |
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Oh, and don't forget that there is a magic sysrq that triggers a |
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panic. Only issue with that is that you'll have to hunt around for |
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whatever caused the actual hangup because it won't be in the panic |
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backtrace (that will just lead you to the sysrq code). |
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> As I expected about the logs. If the machine's dead then I don't want |
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> stuff getting written to disk anyway. kdump sounds like the best |
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> solution going right now. I'll try and see if I can get it working. |
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Yeah - one of these days I'll see if I can get kdump working again. |
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What it really needs is an initramfs that will automatically capture |
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the dump and reboot. That's how other distros handle it. The dumps |
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are pretty big though - the size of your RAM. |
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If you get a dump there are a bunch of tools that can be used to analyze it. |
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Rich |
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